1. Field of the Invention
This invention relates to laminates having metallic or non-metallic facers and polymer foam cores and is more particularly concerned with laminates having polyisocyanurate foam cores.
2. Description of the Prior Art
The preparation of laminates having rigid or flexible facers such as aluminum foil, sheet steel, gypsum board asphalt-saturated felt, wood, kraft paper, and the like, and polyisocyanurate foam cores is well-known in the art; see, for example, U.S. Pat. Nos. 3,940,517; 4,024,310; 4,025,687; and 4,204,019. In order to obtain good adhesion between the facer sheets and the foam core it is generally necessary to expose the laminate to relatively high temperatures, of the order of about 160.degree.-250.degree. F. or higher, for a period of time (of the order of 1-20 minutes). This requires the consumption of significant amounts of energy both when the laminates are being produced continuously using high speed production equipment or when individual panels are being produced in a batch type molding operation.
We have now found that the curing temperature required to ensure good adhesion between skin facers and foam core can be substantially reduced by introducing carefully controlled quantities of organic dipolar aprotic solvents into the polyisocyanurate foam forming reaction mixtures employed in the preparation of the laminate core. We have also found that such introduction of organic polar solvents has additional benefits which will be discussed in more detail hereafter.
The introduction of certain organic polar solvents into polyisocyanurate foam forming mixtures, for example as a part of the catalyst component, has been described hitherto but the amounts so introduced have been significantly less than the amounts required in the present context; see, for example, U.S. Pat. Nos. 3,625,872; 3,746,709; 3,849,349; 3,896,052; 3,903,018; 4,033,908 and 4,071,482.